1. Define two variables as given below (define str "helloworld") (define i 5) Create an expression such that places "_" at position i. For example, the resulting string is "hello_world" according to the given values. Assume that str="BilgiUniv" and i-3, the result is "Bil_giUniv". Test your expression with different str and i values to validate that it works properly. 2. Run the followings and make sure you understand the value expressions: (circle 100 "solid" "red") (place-image (circle 100 "solid" "red") 10 40 (rectangle 200 300 "solid" "green")) (empty-scene 200 200) (place-image (circle 100 "solid" "red") 10 40 (empty-scene 200 200)) 3. Draw the following image. Make sure that your code is written clean and readable